For example, JP 2007-266134A describes a semiconductor device with an IGBT element used as a switching element for an inverter or the like. The semiconductor device has a semiconductor substrate forming a drift layer, and two types of partial regions at a front surface of the semiconductor substrate.
Each of the first-type partial regions includes a P-type first body region, an N+-type emitter region and a P+-type first body contact region. The N+-type emitter region and the P+-type first body contact region are formed at a surface layer portion of the first body region. Each of the second-type partial regions has a P-type second body region and a hole stopper layer. The hole stopper layer is formed such that the P-type second body region is divided into a first part adjacent to the front surface of the semiconductor substrate and a second part adjacent to the bottom of the second body region.
That is, the first body region is not formed with the hole stopper layer, and the second body region is not formed with the emitter region. The first body region of the first-type partial region serves as a channel region, and the second body region of the second-type partial region serves as a thinning-out region. The first-type partial regions and the second-type partial regions are alternately arranged in a planer direction along a surface of the semiconductor substrate. Such a semiconductor device is referred to as a thinned-out semiconductor device. In the described semiconductor device, a collector layer is formed along a rear surface of the semiconductor substrate.
In such a semiconductor device, holes injected from the collector layer is accumulated by the hole stopper layer. Therefore, it is possible to increase a hole concentration of the drift layer. Because conductivity modulation is enhanced in the drift layer, an on-state voltage can be reduced. In the second-type partial region having the hole stopper layer, since the emitter region is not formed, a parasitic transistor is not formed. Therefore, it is less likely that latch-up will occur.